1. Field of the Invention
The present invention relates to a generator control circuit of a vehicle ac generator which includes a voltage regulator, an alarm and an alarm controller.
2. Description of the Related Art
The vehicle ac generator generally supplies electric power to a battery and various electric devices which are mounted in a vehicle. For this purpose, the ac generator is equipped with a voltage regulator for regulating the output voltage of the ac generator at a desired level. Such a generator includes an alarm controller which warns a driver of a trouble of the generator such as a breakdown of the field coil thereof by an alarm lamp, as disclosed in JP-A-10-225008 or its counterpart U.S. Pat. No. 6,075,348. The disclosed alarm controller detects one of phase voltages that are generated in a plurality of phase coils. The detected phase voltage is smoothed by a smoothing capacitor to be compared by a comparator, as an input signal, with a threshold voltage. The alarm lamp is turned off to inform the driver of normal operation of the generator if the smoothed voltage is higher than the threshold voltage.
However, if leak current flows from the battery to the phase coils, the voltage of the input signal of the comparator may be high enough to make the alarm lamp turn off although the phase coils do not generate a normal voltage. Therefore, it is necessary to provide an additional circuit which prevents the above problem. For example, the additional circuit controls the smoothing capacitor to be charged only when the frequency of the phase voltages is higher than a preset level. This makes it difficult to reduce the size of the generator.